As known epitaxial growth methods in which compound semiconductor substrates are manufactured by epitaxially growing compound semiconductor function layers on substrates in order, there are a method which includes a selective growth step at which a mask made of SiO2 or the like is formed on a compound semiconductor function layer grown on a substrate, and then, subsequently, a compound semiconductor layer is epitaxially grown at places where no mask is formed at the same temperature as that at the epitaxial growth step performed before the formation of the mask (see, for example, JP-A No. 11-204829) and a method which includes a selective growth step at which a mask made of SiO2 or the like is formed on a compound semiconductor function layer grown on a substrate, and then, subsequently, a compound semiconductor layer is epitaxially grown at a temperature which is higher than that at the epitaxial growth step performed before the formation of the mask (see, for example, JP-A No. 6-5514). Compound semiconductor substrates with pn junction (which includes p-i-n junction where an spacer layer sandwiched between a p-type layer and a n-type layer is present) are manufactured by using such manufacturing methods including the selective growth steps (hereinafter referred to as “selective growth method”).
Compound semiconductor substrates are used for the manufacture of compound semiconductor devices such as Field Effect Transistors (FETs), Hetero Bipolar Transistors (HBTs), Laser Diodes (LDs), and Photo Diodes (PDs). In terms of an improvement in performance, these compound semiconductor devices are required to have improved electrical characteristics, and compound semiconductor substrates used for the manufacture of such compound semiconductor devices are also required to have excellent electrical characteristics.